DH and I were "teaching" my DD and her BF how to load a dishwasher tonight, and we started discussing what it meant when something said TOP RACK DISHWASHER SAFE. In particular, we were talking about the top to a plastic pizza container, think Rubbermaid. Ok, the water temp is the same, so what is the difference? Water force that hits the dishes? Would that matter for plastic? What are your views? Edited to add that the only other thing we can think of is the heating element at the bottom of the dishwasher???